Method of making gasketed closures



Dec. 17, 1968 c. w. SIMONS ET AL. 3,417,177

METHOD OF MAKING GASKETED CLOSURBS Filed March 9, 1966 BAND OF HEAT- SHRI N KABLE MATERIAL APPLY BAND TO CUP RELEASE BAND HEAT BAND TO SHRINK IN PLACE FIG.|

' INVENTORS CHARLES W. SIMONS JOEL A. GRIBENS Kw W AGENT 3,417,177 METHOD OF MAKING GASKETED CLOSURES Charles W. Simons, Bedford, and Joel A. Gribens, Methuen, Mass., assignors to W. R. Grace & Co., Cambridge, Mass., a corporation of Connecticut Filed Mar. 9, 1966, Ser. No. 533,066 7 Claims. (Cl. 264230) ABSTRACT OF THE DISCLOSURE Sealing gaskets are formed on aerosol mounting cups by positioning a circular band of heat-shrinkable material over a portion of the skirt of the cup and thereafter heating the cup to shrink the band of material into frictional contact with the skirt. Suitable heat-shrinkable materials include stretch-oriented polyolefins, vinyl resins, polyester resins, and natural and synthetic rubber.

This invention pertains to a method of making gasketed closure elements and in particular, relates to a method of producing gasketed mounting cups for pressurized aerosol containers.

Aerosol dispensing containers have found widespread use in the packaging of fluid materials including a variety of both liquid and powdered particulate products. Such containers are provided with a valve-controlled discharge orifice and operate by the action of a volatile propellent which is confined within the container together with the product to be dispensed. Because the propellent has an appreciable vapor pressure at room temperature, the product in the closed container is maintained under superatmospheric pressure. When the valve is opened, the propellent forces the product upwardly through the discharge orifice.

A typical aerosol unit comprises a hollow cylindrical container which is tightly closed at one end and is provided with an opening at its opposite end for receiving a dispensing valve assembly. A mounting cup serves as a closure for the container and also as a support for the valve assembly. The mounting cup comprises a panel having an aperture for receiving the valve assembly, a skirt depending from the periphery of the panel, and an annular channel extending outwardly from the lower edge of the skirt. When the cup is inverted in sealing position on the container, the channel is positioned over the bead surrounding the container opening and the lower portion of the skirt adjacent the channel is flared outwardly against the container wall adjacent the bead. To ensure adequate sealing between the closure and the container, the cup is provided with a gasket which may reside in the annular channel or predominantly in the channel f the cup. Preferably, however, the gasket is positioned exclusively on the lower portion of the skirt so that when the cup is crimped on the container, the gasket forms a seal in the seam produced between the skirt and the container wall.

The method most commonly employed in preparing mounting cup gaskets has consisted of forming the gaskets in situ from liquid gasket-forming compositions comprising an elastomer dispersed or dissolved in a volatile organic liquid vehicle. In the manufacture of these gaskets, the liquid composition is deposited in the desired configuration in the cup while the cup is being rotated beneath a metering nozzle through which the composition flows. The deposit is then converted into a dry solid sealing mass by expelling the liquid vehicle at elevated temperatures.

Though the technique of flowing gaskets into place has been extremely efiicient and is used commercially today, it is still desirable to achieve further improvements in the United States Patent "ice art of mounting aerosol gaskets, for example, by further simplifying the mechanical operations involved and providing greater latitude in the types and choice of sealant materials employable.

According to the present invention, a method is provided wherein gaskets can be applied to aerosol mounting cups in a rapid, simple and efficient manner to form gasketed closures exhibiting excellent sealing performance. Specifically, the present invention provides a method of applying a gasket to an aerosol mounting cup comprising a top panel, a skirt depending from the periphery of the top panel and an annular channel extending outwardly from the bottom edge of the skirt which comprises positioning a band of gasketing material over the outside surface of the skirt so that its lower edge overlies the juncture where the skirt and channel merge, said gasket consisting of a circular band of heat-shrinkable material having a diameter slightly greater than the outside diameter of the skirt of the cup but less than the inside diameter of the annular channel, and heating the cup carrying the positioned band of material at a temperature and for a time sufiicient to shrink the band of material into frictional engagement with the skirt.

The present invention will be more clearly understood from a reference to the attached drawings and the discussion relating thereto:

FIGURE 1 schematically illustrates the present method of fabricating gasketed aerosol mounting cups.

FIGURE 2 shows in axial section a gasketed cup prepared according to the method of FIGURE 1.

FIGURE 1 shows the successive steps employed to apply the gasket. In general, there is first provided a circular band of material capable of being heat shrunk into circumferential contact with the closure skirt. The band of material which has a diameter slightly larger than the outside diameter of the skirt of the cup but less than the inside diameter of the annular channel of the cup is slipped over the outside surface of the skirt of the cup and then released in a position so that its lower edge overlies the juncture where the skirt and channel merge. Thereafter, the cup carrying the positioned band of material is heated at a temperature and for a time suflicient to shrink the band into tight frictional engagement with the skirt.

FIGURE 2 is an axial sectional view of the gasketed mounting cup shown in inverted position relative to its placement in the assembled container and produced according to the steps illustrated in FIGURE 1. The cup, generally designated at 10, comprises a circular panel 11 having an integral skirt 12 depending from its periphery. The free edge of skirt 12 is outwardly flanged at 13 to form an annular channel 14 for embracing the bead surrounding the container opening (not shown) when the cup is positioned thereon. The inner portion of panel 11 is countersunk to form a tubular recess, generally designated at 16, which has a dependent circular wall 17 integrally joined with an :apertured horizontal wall 18. When the cup is placed in sealing position, the tubular recess 16 acts as a pedestal for the valve unit and the valve stem is admitted into the container through iapertured wall 18.

Gasket 19 is disposed on the exterior surface of the skirt 12 and extends upwardly for a distance from the skirtchannel juncture 13 to approximately the midpoint between the top panel 11 and the juncture 13. This portion of the cup between the midpoint of the skirt 12 and its juncture 13 with the channel 14 is commonly referred to in the aerosol art as the shoulder of the cup.

As indicated above, the band of material employed must be capable of shrinking sufli-ciently when heated to form a reasonably tight friction fit with the closure skirt. Otherwise, it will stlip out of sealing position when the cup is inverted and placed over the mouth of the container prior to crimping. In addition, the band of material after shrinking must provide a gasket which is sufficiently deformable under the pressure encountered during crimping to flow into and fill the tiny passages or voids in the seam without cracking.

Bands having these characteristics may be composed of stretch-oriented, heat-shrinkable materials, such as polyolefins, e.g. polyethylene and polypropylene; vinyl resins, e.g. polyvinylidene fluoride, polyvinylidene chloride, polystyrene and polyvinyl chloride; polyester resins, e.g. polyethylene terephthalate; rubber derivatives, e.g. rubber hydrochloride; and elastomeric compositions containing a large-amount of wax, e.g. natural and synthetic rubber containing a large amount of petroleum wax. Such materials may be stretch-oriented uniaxially or biaxially. When the material employed is stretch-oriented in Only one direction, the orientation must be in a circumferential direction in the band fabricated therefrom. Materials, such as oriented polyolefins, may be irradiation or chemically cross-linked, if desired.

The bands may be prepared from the heat-shrinkable materials in any convenient manner. For example, bands of suitable dimensions may be cut from tubing stretchoriented laterally or stretch-oriented both laterally and longitudinally, or bands may be cut from tubing capable of being stretch-oriented. In the latter instance, the individual bands after being cut are stretch-oriented cincumferentially; and, if desired, also stretcher-oriented in a direction perpendicular to the circumference.

The exact dimensions required for the band of heatshrinkable material will depend upon the size of the closures employed. Regardless of closure used, however, the diameter of the band of heat-shrinkable material must be larger than the outside diameter of the closure skirt but less than the inside diameter of the channel so that it can be readily slipped over the outside surface of the skirt into sealing position and yet maintained in place on the skirt by the outwardly flanged annular channel. The mounting cups commonly used with conventional aerosol cans have a skirt diameter (outside diameter) of about 0.991 inch since the cans have a standard filling opening of 1.000: 0.004 inch The inside diameter of the channel of the cup is about 1.253 inches. Thus, for standard cups the heat-shrinkable band should have an inside diameter between about 0.995 and 1.250 inches.

The width and the thickness of the heat-shrinkable bands employed are substantially the same as the width and thickness desired in the assembled gaskets since the change in these dimensions upon heat shrinking of the band are negligible. To provide an effective and lasting seal, the gasket should cover the shoulder of the cup since this part of the closure is flared outwardly and forced against the container wall adjacent the container opening when the cup is crimped on the container. Therefore, the band of heat-shrinkable material should be wide enough to cover that portion of the skirt extending between the skirtchannel juncture and about the midpoint of the skirt between the top panel and the skirt-channel juncture. Though the band may be wider so that the gasket extends above the skirt midpoint, no further benefit is achieved with respect to scaling.

The thickness of the heat-shrinkable band used on standard cups should be between about 2 and mils in order to give a gasket thickness in this range. A thickness of at least 2 mils is necessary to assure that enough material is present to completely seal the irregularities in the crimped seam produced betwen the skirt and the container walls. Above about 10 mils, the gasket may be damaged when the closure is placed on the container in instances where tolerances between the closure skirt and container opening are very close.

The apparatus used in carrying out the present method may be of any design suitable for applying and positioning the band on the closure. To shrink the band in place, the cup carrying the positioned band may be placed in an oven or heat applied to the assembly in any other convenient manner. The exact temperature and time required for shrinking the band will depend upon the particular material employed. Generally, one to three minutes at about 240 F. is sufficient for oriented wax-rubber compositions and other oriented materials, such as polyolefins, and polyvinyl or polyvinylidene halides which may or may not be cross-linked. However, in all cases the cup carrying the band must be heated at a temperature and for a time sufficient to shrink the band of material into circumferential engagement with the closure skirt.

The following examples are given to further illustrate the present invention.

EXAMPLE 1 Several aerosol mounting cups having gaskets placed exclusively on the shoulder of each closure were prepared as follows. Polyethylene tubing having an inside diameter of 0.875 inch and a wall thickness of 7.5 mils was cut into segments about 0.185 inch wide. Each of the resulting polyethylene bands was stretch-oriented circumferentially to a diameter of about 1.063 inches and then positioned over the outside surface of the skirt of a cup so that its lower edge overlays the juncture where the skirt and channel merge. Thereafter, the cups carrying the positioned bands of polyethylene were heated at 240 F. until each band had shrunk sufficiently to frictionally engage the closure skirt. About 2 to 3 minutes was required for obtaining a tight friction fit.

The closures employed where those commonly used for test purposes where the aperture in the horizontal pedestal wall for receiving a valve unit is omitted. A valve mechanism is not employed on test packs due to weight loss through the valve. The cups, otherwise, were standard in design and dimensions and had a skirt diameter (outside) of about 0.991 inch and a channel diameter (inside) of about 1.253 inches.

In all of the closures produced, the gaskets extended from the skirt-channel juncture to approximately the midpoint of the skirt between the top panel and skirt-channel juncture. The thickness of each of the gaskets was about 7.5 mils.

When the performance of the gaskets was tested at conventional crimps on a standard propellent pack consisting of a mixture of 60 parts by weight trichloromonofluoromethane (Freon 11) and 40 parts by weight dichlorodifluoromethane (Freon 12), it was found that all of the gasketed closures prepared according to the above method gave satisfactory mechanical seals. The average weight loss after one day for this group of cups was 0.003 gram as based on an initial quantity of propellent ranging between about 20 and 45 grams. In comparison, test packs closed with aerosol mounting cups without gaskets showed a total loss of propellent in one day.

Another batch of cups gasketed with polyethylene was prepared in the same manner except that the polyethylene tubing had a wall thickness of about 2.0 mils. When these gaskets were tested according to the procedure described above, the average weight loss for the batch was 0.009 gram per day.

The maximum permissible weight loss for acceptable mechanical sealing with the above propellent is set at 0.015 gram per day since this value represents the amount of Freon l1/ Freon l2 propellent ordinarily lost through the valve assembly on commercial packs during the same period.

EXAMPLE 2 A group of several aerosol mounting cups having gaskets positioned exclusively on the shoulder of the closures was prepared using biaxially oriented, irradiation cross-linked polyvinylidene fluoride tubing. The tubing had an inside diameter of 1.06 inches, a wall thickness of 7 mils, and was capable of shrinking at least about 20% in diameter in the presence of heat. The closures used were of standard dimensions similar to those employed in Example 1.

In preparing the gasketed closures, bands of material of sufiicient width (about 0.185 inch) to cover the shoulder of the closures were cut from the polyvinylidene fluoride tubing. Each band of material was placed over the outside surface of the skirt of the cup and released so that its lower edge overlay the juncture where the skirt and channel merge. The band was then heat shrunk into frictional engagement with the closure skirt by placing the cup carrying the positioned band in an oven maintained at 240 F. for about 2 to 3 minutes.

In the resulting closures, the gaskets formed a tight frictional fit with the skirt and extended from the skirtchannel juncture to about the midpoint of the skirt. The thickness of each gasket was about 7 mils.

When the performance of the gasketed closures was tested on Freon 11/ Freon 12 packs as in Example 1, the average loss for the group of closures after one day was 0.007 gram.

EXAMPLE 3 A group of several aerosol mounting cups having shoulder gaskets were prepared in the same manner as in Example 1 above except that the tubing employed had an inside diameter of 0.750 inch, a wall thickness of 8 mils, and was composed of a composition consisting of 100 parts by weight polyvinyl chloride, 40 parts by weight dioctyl adipate and 40 parts by weight dioctyl phthalate. After being stretch-oriented, the bands of material had a diameter of about 1.063 inches. The width of each band was about 0.185 inch.

As in Example 1, the gaskets produced when the bands were heat shrunk into frictional engagement with the closure extended from the skirt-channel juncture to about the midpoint of the skirt. The thickness of each gasket was about 8 mils.

When tested on Freon 1l/Freon l2 propellent packs as in Example 1, the average weight loss of this group of gasketed cups was 0.004 gram after one day.

EXAMPLE 4 Several gasketed aerosol mounting cups were prepared using the same procedure as in Example 1 by orienting circular bands cut from tubing capable of being stretchoriented. The tubing employed was composed of 100 parts by weight natural rubber, 40 parts by weight paraffin wax and 5.0 parts by weight zinc oxide cured with 2 parts by weight sulfur and 2 parts by weight zinc dibutyl dithiocarbamate. The tubing had an inside diameter of 0.750 inch and a wall thickness of 8 mils. The bands out therefrom had a width of about 0.185 inch and were stretchoriented to a diameter of 1.06 inches.

After being slipped over the outside surface of the cup and released in sealing position, the cups carrying the bands were heated for 2 to 3 minutes in an oven maintained at a temperature of 240 F. to shrink the bands into tight circumferential engagement with the shoulder of the cups.

The resulting gaskets had a thickness of 8 mils and were coextensive with the lower portion of the skirt extending between the skirt-channel juncture and skirt midpoint.

When tested on packs of Freon 11/ Freon 12 as in Example 1, the average weight loss for the gasketed closures was 0.007 gram after one day.

It is apparent from the above examples that the present invention offers a rapid and simple method of preparing gasketed aerosol mounting cups where the gasket is positioned exclusively on the shoulder of the closure. The bands of material used for the gaskets may be easily fabricated, for example, by cutting segments of suitable width from commercially available heat-shrinkable tubing having the necessary diameter and thickness. The resulting bands may be positioned on the cups quickly and accurately to give uniform and elfective seals without concern for variations in or displacement of the gasket during handling or on the pack.

We claim:

1. A method of applying a gasket to an aerosol mounting cup comprising a top panel, a skirt depending from the periphery of the top panel and an annular channel extending outwardly from the bottom edge of the skirt which comprises positioning a band of gasketing material over the outside surface of the skirt so that its lower edge overlies the juncture where the skirt and channel merge, said gasket consisting of a circular band of heat-shrinkable material having a diameter between about 0.995 and 1.250 inches and a wall thickness between about 2 and 10 mils and said gasket dimensions being related to a mounting cup wherein the skirt has an outside diameter of about 0.991 inch and the annular channel has an inside diameter of about 1.253 inches, and heating the cup carrying the positioned band of material at a temperature and for a time sufficient to shrink the band of material into frictional engagement with the skirt.

2. A method according to claim 1 wherein said band of gasketing material is of sufficient width to cover the skirt between its midpoint and its juncture with the channel.

3. A method according to claim 2 wherein said band of gasketing material is shrunk into frictional engagement with the skirt by heating at 240 F. for 1 to 3 minutes.

4. A method according to claim 3 wherein said band of gasketing material is composed of stretch oriented, irradiated polyvinylidene fluoride.

5. A method according to claim 3 wherein said band of gasketing material is composed of stretch-oriented polyethylene.

6. A method according to claim 3 wherein said band of gasketing material is composed of stretch-oriented polyvinyl chloride.

7. A method according to claim 3 wherein said band of gasketing material is composed of a stretch-oriented cured natural rubber composition containing 40 parts by weight parafiin wax as based on parts by weight rubber.

References Cited UNITED STATES PATENTS 3,004,297 10/1961 Stover 264-230 3,345,227 10/1967 Park 264-259 3,182,864 5/1965 Ellis et al. 2393.37

JULIUS FROME, Primary Examiner.

J. R. THURLOW, Assistant Examiner.

US. Cl. X.R. 239 337; 264-268 

